The present invention relates to very small-flow-range fluid applying apparatus and fluid applying method required in such fields as information/precision equipment, machine tools, and FA (Factory Automation); or in various production processes of semiconductors, liquid crystals, displays, surface mounting, and the like, and also relates to a plasma display panel formed by the fluid applying method and a pattern formation method therefor.
Issues related to conventional printing techniques are explained below by taking as an example a technique for forming the fluorescent substance layer of plasma display panels (hereinafter, referred to as PDPs).
A PDP that performs color display has, on its front-face plate/rear-face plate, a fluorescent substance layer composed of fluorescent substance materials that emit light in RGB (red, green, blue) colors, respectively. This fluorescent substance layer is so structured that three stripes which are filled with fluorescent substance materials of RGB colors, respectively, are formed between partition walls formed in parallel lines on a front-face plate/back-face plate (i.e., on an address electrode), and arrayed in a multiplicity with the three sets of the stripes parallelized in adjacency. This fluorescent substance layer is formed by a screen printing method, or photolithography method or the like.
With the conventional screen printing method, a large-scale screen makes it hard to achieve high-precision alignment of the screen printing plate, and in filling the fluorescent substance materials, the materials might be placed even on the top portions of the partition walls. As a result, it has been necessary to take measures such as introduction of a polishing process for removing the placed materials. Further, since the amount of filled fluorescent substance material varies depending on the difference in squeegee pressure, pressure control therefor is extremely subtle work, which largely depends on the degree of the skill of the operator. Thus, it is quite hard to obtain a constant filling amount over the entire front-face plate/back-face plate.
It is also possible to form the fluorescent substance layer by the photolithography method with the use of photosensitive fluorescent substance materials. However, this necessitates exposure and development steps, involving a number of steps larger than that of the screen printing method, giving rise to an issue of increased manufacturing cost.
Now, “direct patterning method” has recently been receiving attention in various fields in view of simplification, cost reduction, environmental load reduction, resources saving, energy saving, and the like of manufacturing processes. For example, there have been proposed engineering techniques taking advantages of individual methods including:
{circle around (1)} Dispenser method,
{circle around (2)} Ink jet method,
{circle around (3)} Electric-field jet method, etc.
A direct patterning method using a dispenser has already been proposed to solve the above-described issues in order to form the screen stripes in manufacturing processes of PDPs, CRTs, and the like in Japanese examined patent publication No. S57-21223 and Japanese unexamined patent publication No. H10-27543. According to this proposal, only setting numerical values of substrate specifications allows fluorescent substance to be discharged from a nozzle moving on the substrate and to be applied into grooves between ribs without the use of any conventional screen mask, so that the fluorescent substance layer can be formed with high precision for substrates of arbitrary sizes, while changes in substrate specifications can readily be managed. In the case of dispensers, the line width of drawing lines is restricted by the size of the inner diameter of the discharge nozzle. Since reducing the nozzle diameter to thin the line width would cause the clogging to more frequently occur, the line width would be limited to at most 70 to 100 μm.
Meanwhile, it has been under development that the ink jet method developed for consumer printers is applied to applying apparatuses for industrial equipment. However, this method is, at the present stage, capable of treating only low-viscosity fluids of about 10 mPa·s and incapable of managing high-viscosity fluids from the driving method and structural constraints. Further, the powder diameter that can be prevented from clogging of the flow passage is limited to about 0.1 μm, posing large constraints in terms of material. In addition, the fluid to be used as the applying material is, in many cases, a high-viscosity powder and granular material containing fine powder with its outer diameter ranging from 0.1 micron to tens of microns, such as electrode material, fluorescent substance material, solder, and electrically conductive capsules. With a view to draw fine electrode lines by using the ink jet method, there has been developed a nanopaste in which Ag particles having a mean particle size of about 5 nm are independently dispersed with the Ag particles covered with a dispersant.
However, also in this case, because the ink jet method is only capable of treating a low-viscosity nanopaste, the drawing lines would result in smaller thicknesses, causing the wiring resistance to become high. As a result, overstrikes would be required to ensure the thickness, posing an issue in terms of production cycle time.
In order to solve the above-described issues related to the dispenser method and the ink jet method, there have been proposed applying apparatuses for high-viscosity fluids called electric-field jet method (see Japanese unexamined patent publications No. 2000-246887 and No. 2001-137760). This method is based on the discharge method using electric field reported by Zeleny in 1917.
Referring to a principle view of FIG. 31, reference numeral 500 denotes a high-viscosity fluid, 501 denotes a control section, 502 denotes a container, 503 denotes an opening, 504 denotes an electrode, 505 denotes a power supply, 506 denotes an application-object base material (a substrate which is an object of application), 507 denotes an elongated portion of the applying fluid having flowed out from a nozzle, and 508 denotes a pressurization device. This applying apparatus has the opening 503 such as a circular or polygonal orifice or nozzle with a hole diameter of about 50 μm to 1 mm φ, at a lower portion of the container 502, and the electrode 504 is placed at a portion of this opening 503. Within the container 502 is filled the high-viscosity fluid 500 with a high-viscosity substance of 1,000 to 1,000,000 cps as a liquid applying material. In order to pressurize the high-viscosity fluid 500 filled in the container 502, the pressurization device 508 by high-pressure air is provided so as to be connected to the container 502. First, pressure is applied to the high-viscosity fluid 500 within the container 502, by which a meniscus of the high-viscosity fluid 500 is formed at the opening 503. Next, a first specified pulse voltage is applied to between the electrode 504 of the nozzle opening 503 and the application-object base material 506 that is the counter electrode so that the meniscus of the high-viscosity fluid 500 is elongated longitudinally at the opening 503, thereby forming the elongated portion 507, in which state the high-viscosity fluid 500 is let to drop from the tip end of this elongated portion. In this state, moving the nozzle and the application-object base material 506 relative to each other allows ultrafine lines of 10 μm or less to be drawn because the tip end of the meniscus has become sufficiently thinner than the nozzle diameter.
Further, applying a second specified pulse voltage to between the opening 503 and the application-object base material 506 allows the elongated portion 507 to be partly separated from its tip end, by which the application of the high-viscosity fluid 500 can be interrupted. By this electric-field jet method, it becomes possible to draw ultrafine lines equivalent to those of the ink jet method by using high-viscosity fluids that could not be treated by the ink jet method.
However, this electric-field jet method has had the following issues. With the electric-field jet method, since a small rate of flow is transported from the container 502 to the nozzle tip end by the capillary phenomenon, the discharge of fluid can be achieved only by the electric field without using the pressurization device 508. Nevertheless, in the case where application lines of a fluorescent substance or electrode material are continuously applied onto a substrate (e.g., front-face plate or back-face plate of a PDP) placed, for example, on a stage (see, e.g., a mount plate 50 and an X-Y stage 50x in FIG. 26) that runs at high speed, it is necessary to apply both electric field and air pressure to ensure the flow rate. In this case, this method has two types of characteristics, those of the air type dispenser and those of the electric-field jet method, in combination at the same time. That is, the method bears the following shortcomings of the air type dispenser:
{circle around (1)} Poor stability of application flow rate; and
{circle around (2)} Incapability of forming starting and terminating ends of continuous lines at high grade.
The above {circle around (1)} is due to a reason that the discharge flow rate of the air type dispenser is inversely proportional to the viscosity of the applying fluid. Also, the viscosity of the fluid depends largely on temperature. For example, in the case of a standard calibration liquid, the viscosity changes to 50% due to a 5° C. change of the fluid temperature. In the case of the air type dispenser, as great care is necessary to maintain the liquid temperature constant in order to reduce flow rate drifts, so similar care is necessary also for the electric-field jet method that uses air as an auxiliary pressure source.
The above {circle around (2)} is due to poor responsivity of the air type dispenser. This shortcoming can be attributed to the compressibility of air encapsulated in a cylinder and the nozzle resistance resulting when the air is let to pass through a narrow gap. That is, with the air method, because of a large time constant of the hydraulic circuit that depends on the cylinder capacity and the nozzle resistance, a time lag of 0.07 to 0.1 second has to be allowed for a time period which, after application of an input pulse, lasts from when the fluid starts to be discharged until when the fluid is transferred onto the substrate, or until when the fluid is interrupted during continuous application.
In the case of the electric-field jet method, as described before, the discharge can be interrupted only by electric field without the use of the pressurization device 508 using air pressure. However, with the use of the pressurization device 508 using air pressure for obtainment of larger application flow rates, starting and terminating ends of the continuous application line cannot be drawn at high grade because of the poor response of the air type. For example, at a starting end of a drawing line, even if an air pressure is applied simultaneously with application of a voltage at a start of application, the air pressure cannot be immediately increased to a specified pressure. As a result, there occurs ‘thinning’ or ‘cut’ at the starting point of the drawing line. Otherwise, at the terminating end of a drawing line, even if the air pressure is lowered simultaneously with turn-off of the voltage at a start of application, the air pressure cannot be immediately dropped to a specified pressure. As a result, there occurs ‘thickening’ or ‘gathering’ at the terminating end of the drawing line.
An object of the present invention is to provide fluid-applying apparatus and fluid-applying method as well as a plasma display panel and a pattern forming method therefor all of which are good at stability of application flow rate and capable of forming starting and terminating ends of application lines at high grade.